ARRL Propagation Bulletin ARLP030 (2006)

ARLP030 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 30  ARLP030
From Tad Cook, K7RA
Seattle, WA  July 28, 2006
To all radio amateurs 

ARLP030 Propagation de K7RA

There wasn't much change this week from last, with average daily
sunspot numbers down slightly, less than five points to 14.6.  This
doesn't result in high enough MUF values to see much propagation on
the highest HF bands, such as 10, 12 and 15 meters.  But even with a
low MUF, there is still occasional long distance propagation on 10
and 6 meters.

Larry Godek, W0OGH of Gilbert, Arizona says he monitors 6 and 10
meter FM all day.  Larry scans many channels on both bands with
multiple receivers.  On 29.62 MHz, he often hears W1OJ in Boston and
another repeater in Florida, although not so much recently.  Lately
he hears quite a bit of W5DFW in Dallas on 29.66 MHz.  On Tuesday,
July 25 Larry was hearing W5DFW, alternating with a California
station.  On the same day he heard a repeater on 53.09 MHz, but
didn't catch the ID.  He suspects it was in Oklahoma or Texas.  He
also heard stations near Sacramento, California.

For parsing those mystery signals, Larry wishes he had a database of
six and ten meter FM repeaters that he could sort by frequency.
Ideally, it would cover all of North America, so he wouldn't need to
look through separate state lists.

Joe Alvin, KB1JVW of White River, Vermont asks for some comments on
how current sunspot numbers affect MUF, or Maximum Usable Frequency.
Generally MUF is lower with lower sunspot numbers, but there is
quite a bit of variation depending on where the two ends of the
communication path are located.  For instance, from Joe's location,
the MUF recently (calculating from average sunspot numbers using a
propagation prediction program) on a path to Germany would vary from
13.3 MHz at 0300z to a peak above 17 MHz from 1500-1530z and
1830-2030z, and up to 17.4 MHz around 0000z.  But with the same
sunspot number on the same date, the path from Dallas to Costa Rica
would show an MUF that peaks above 24 MHz from 2330-0230z and dips
below the 20 meter band around 0900-0930z.  A few years from now, if
the sunspot number rises to around 100, that path from Dallas to
Costa Rica would peak above 28 MHz from 1730-2200z and around 0200z.

Over the next week, don't expect any huge increase in sunspot
numbers.  We are near the bottom of the solar cycle, and in the
summer season, which is not as interesting as fall or spring for
working long distances.  But if the predictions are correct, a
little over a year from now the sunspot count should be heading
higher than it is now, and the MUF will rise with it.

Dean Wilmoth, KC0SRM of Sturgeon, Missouri asks about trends over
the next weeks and months.  Sunspot numbers will still be low, and
will head lower, but of course seasonal effects will change.  For a
path from his area to Central America, for instance, 20 meters will
prove more reliable than 17 meters or higher.  But move that out two
months, and 20 meters will be closing earlier, and 17 meters will be
more useful during the day than it is now.  Also, with longer nights
and less seasonal noise from thunderstorms both near and far, 80 and
40 meters will improve in the fall compared to summer.

Currently, early Friday, July 28 there is a strong solar wind stream
hitting Earth, and the planetary K index is at six.  This should
decline over the next couple of days, but then come back again on
Tuesday.  Lower geomagnetic indices generally mean better HF
propagation, or at least not as poor as it is commonly when the K
index is high.  The predicted planetary A index for Friday through
Tuesday, July 28 to August 1 is 15, 5, 5, 12 and 20.

If you would like to make a comment or have a tip for our readers,
email the author at,

For more information concerning radio propagation, see the ARRL
Technical Information Service at For a detailed
explanation of the numbers used in this bulletin, see An archive of past
propagation bulletins is at .

Sunspot numbers for July 20 through 26 were 14, 12, 0, 21, 19, 16
and 20 with a mean of 14.6. 10.7 cm flux was 72.2, 72.6, 73.6, 76.5,
77, 75.5, and 74.7, with a mean of 74.6. Estimated planetary A
indices were 3, 2, 4, 4, 4, 6 and 6 with a mean of 4.1. Estimated
mid-latitude A indices were 2, 1, 3, 4, 7, 5 and 5, with a mean of